High temperature metallic seal

ABSTRACT

A metallic seal includes a cold formed substrate layer and one or more additional layers. At least one of the layers offers improved resistance to high temperature stress relaxation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional and continuation-in-part application ofU.S. patent application Ser. No. 10/805,764 filed Mar. 22, 2004 andentitled “HIGH TEMPERATURE METALLIC SEAL” which is a divisionalapplication of U.S. patent application Ser. No. 10/002,684 (abandoned)filed Oct. 24, 2001 and entitled “HIGH TEMPERATURE METALLIC SEAL” whichclaims benefit of U.S. Provisional Patent Application Ser. No.60/242,759 filed Oct. 24, 2000 and also entitled “HIGH TEMPERATUREMETALLIC SEAL.” The disclosures of Ser. No. 60/242,759, 10/002,684, and10/805,764 are incorporated by reference herein as if set forth atlength.

BACKGROUND OF THE INVENTION

This invention relates to seals, and more particularly to metallicseals.

A variety of metallic seal configurations exist. Key metallic seals arecommonly held under compression between two opposed flanges of theelements being sealed to each other. Such metallic seals may be used ina variety of industrial applications.

Key examples of such metallic seals are of an annular configuration,having a convoluted radial section which permits the seal to act as aspring and maintain engagement with the flanges despite changes orvariations in the flange separation. Certain such seals have an S-likesection while others have a section similar to the Greek letter Σ withdiverging base and top portions. Other similar seals are formed withadditional convolutions. One exemplary seal is sold by The AdvancedProducts Company, North Haven, Conn., as the E-RING seal. Such seals arecommonly formed as a monolithic piece of stainless steel or superalloy.Such seals are commonly formed from sheet stock into a shape which iseffective to provide the seal with a desired range of compressibilityfrom a relaxed condition. These seals are installed in applications in acompressed state as shown in FIG. 1. The total compression (Δh_(T))consists of an elastic component (ΔH_(EL)) and plastic component(Δh_(PL)) so thatΔh _(T) =Δh _(EL) +Δh _(PL)With continued exposure at elevated temperatures, the plastic componentΔh_(PL) grows resulting from creep and the elastic component Δh_(EL)decreases with time. As a result, the sealing load or the capability ofthe seal to follow the flange movement also diminishes with timeresulting from the reduced Δh_(EL). This phenomenon is called stressrelaxation.

BRIEF SUMMARY OF THE INVENTION

Therefore, long-term applications of current metallic seals aregenerally limited to about 1300° F. because the current cold formablenickel-based superalloys such as INCONEL 718 (Special MetalsCorporation, Huntington, W.V.) and WASPALOY (Haynes International, Inc.,Kokomo, Ind.), lose their strength at temperatures greater than 1300° F.and stress relax because of the dissolution of γ′ precipitates.

There are other cast metallic alloys, such as MAR M247 (a castsuperalloy used in manufacture of turbine engine blades available fromCannon-Muskegon Corporation, Muskegon, Mich., as CM 247) which are usedat ultra high temperatures (about 2000° F. or 1100° C.) for thickcross-section cast and wrought components. These alloys can not readilybe rolled into thinner gauges and cold formed into static seal shapes.

Recently developed mechanically alloyed strips such as MA 754 of SpecialMetals Corporation and PM 1000 of Plansee AG, Reutte, Austria, withsuperior high temperature strength characteristics are also verydifficult to fabricate into seal shapes.

Some of the refractory alloy strips such as molybdenum base (e.g.,titanium-zirconium-molybdenum (TZM)) and niobium base alloys, althoughcold formable, have poor oxidation resistance above 1200° F. (649° C.).Therefore, it is believed that no current metallic alloy can readily becold formed into seal and used at demanding elevated temperatureapplications requiring enhanced stress relaxation resistance.

One aspect of the present invention advantageously combines the coldformability of the current sheet alloys and stress relaxation resistanceof other metallic alloys and composites which are not cold formable.Seal shapes are formed with cold formable alloys and a layer ofcreep/stress relaxation resistant alloys is deposited on the alreadyformed substrate. The substrate can be either a fully formed orpartially formed shape of the seal to achieve any thickness profile onthe strip. Thickness can be preferentially built up in areas with highstress.

The deposition of the creep/stress relaxation resistant layer can beaccomplished by processes such as:

-   thermal spray of molten alloy droplets and powder;-   thermal spray of creep resistant alloys with micron (10⁻⁶ m) and    submicron size ceramic particles such as zirconia, alumina and    silicon carbide;-   vapor deposition such as electron beam physical vapor deposition (EB    PVD);-   slurry coating of ceramics and curing at elevated temperatures;    and/or-   electroforming of high temperature alloys with or without micron or    submicron size ceramic particles.

The resultant metallic composite structure can advantageously befabricated cost effectively to provide complexcreep/relaxation-resistant structures for ultrahigh temperatureapplications. Other high temperature formed structures such as hightemperature ducting, combustor liners and components for gas turbineengines can also be fabricated using this technology. Such structuresmay be advantageous substitutes for more expensive ceramic elements.

A second aspect involves providing an oxidation-resistant coating to astress relaxation-resistant but oxidation-prone substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a radial sectional view of a metallic seal.

FIG. 2 is a radial sectional view of a first metallic seal according toprinciples of the invention.

FIG. 3 is a radial sectional view of a second metallic seal according toprinciples of the invention.

FIG. 4 is a radial sectional view of a third metallic seal according toprinciples of the invention.

FIG. 5 is an enlarged view of the seal of FIG. 4.

FIG. 6 is a graph of test data showing stress relaxation for variousmaterials at 1600° F. (871° C.).

FIG. 7 is a graph of test data showing stress relaxation for variousmaterials at 1800° F. (982° C.).

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

FIG. 2 shows a seal 20 formed as an annulus having symmetry about acentral longitudinal axis 500. In operation, the seal is held incompression between opposed parallel facing surfaces 502 and 503 offirst and second flanges 504 and 505 to isolate an interior volume 506from an exterior volume 507.

The seal is formed as a convoluted sleeve having first and second layers22 and 24 and extending from a first end 26 to a second end 28. In theexemplary embodiment, the first layer 22 is generally interior of thesecond layer 24 and has first and second surfaces 30 and 32. In anexemplary manufacturing process, the first layer 22 is initially formedas a flat strip of cold formable material (e.g., it may be formed into acomplex shape at a temperature which is less than half its Fahrenheitmelting temperature and, preferably, at ambient conditions (roomtemperature)). The ends of the strip may be welded to form a sleeve, thetwo faces of the strip thereby becoming interior and exterior faces ofthe sleeve. The sleeve may be deformed into a convoluted shape such asthat shown in FIG. 2, the interior and exterior sleeve faces becomingthe surfaces 30 and 32, respectively, and the end rim surfaces of thesleeve in part defining the ends 26 and 28. After any optionaladditional further cleaning, machining, or surface treatment, the secondlayer 24 is deposited on the first layer 22. In the illustrated example,the layer 24 is gradually built up on the surface 32 with asubstantially uniform thickness of a similar order of magnitude to thethickness of the layer 22. There may be additional optional machining,polishing, or surface treatment of the layer 24. Typically, however,there will be no additional machining or polishing involved. The resultof this process is the production of an integrated seal in which thelayers are held together not merely by macroscopic mechanicalinterfitting but adhesion at the microscopic level between the innersurface 40 of the layer 24 and the outer surface 32 of the layer 22. Amajor portion of the outer surface 42 of the layer 40 constitutes theexternal surface of the seal in contact with the volume 507. Portions 44and 46 of the surface 42, slightly recessed from the ends 26 and 28,face longitudinally outward and provide bearing surfaces for contactingthe flange surfaces 502 and 503 to seal therewith. Each layer makes asubstantial contribution to the longitudinal compression strength andperformance of the seal. Preferably in an anticipated range ofoperation, each contributes at least ten percent and, preferably, 30%.

Exemplary thermal operating conditions for the seal are in the range of1600-2000° F. (871-1093° C.) or even more. A more narrow target is1700-1900° F. (927-1038° C.). This does not necessarily mean that theseal can not be used under more conventional conditions. Under thetarget operating condition, the coating layer (e.g., the second layer24) has a higher resistance to stress relaxation or creep than does thesubstrate layer (e.g., the first layer 22). Preferably the substratelayer is formed of a nickel- or cobalt-based superalloy. Particularlypreferred materials are WASPALOY and HAYNES 230® (UNS No. N06230).Preferred coatings are cast γ′ hardened nickel-based superalloys.Particularly preferred coating materials are MAR M2000 and MAR M247.FIGS. 6 and 7 show stress relaxation according to the ASTM E-328 testfor various candidate substrate and/or coating materials at low and midtarget temperatures of 1600 and 1800° F. (871 and 982° C.) respectively.

FIG. 3 shows an alternate seal 120 having first and second layers 122and 124. Potentially otherwise similar to the seal 20, the seal 120 hasa more uneven thickness of the layer 124. In particular, the layer 124is relatively thin near the contacting surface portions 144 and 146 nearthe seal ends 126 and 128.

FIG. 4 shows an alternate seal 220 of generally overall similarconfiguration to the seals of FIGS. 1-3. Structurally, the seal consistsessentially of a single layer 222 of a cold formed refractory alloystrip (e.g., TZM). The entire exterior surface of the layer 222 iscovered by a protective coating 224 which is not expected tosubstantially contribute to the strength of the seal. The coating is,however, effective to protect the underlying layer 222 from oxidation atelevated temperatures (e.g., at a target temperature in excess of 1200°F. (649° C.)). A preferred coating is molybdenum disilicide (MoSi₂)applied as a slurry coat followed by baking to produce a fused silicidecoating. One specific silicide-based coating technology is availablefrom Hitemco East, Old Bethpage, N.Y., and is formed by a processincluding the acts of slurry coating and baking the coating at hightemperature.

Another preferred coating is nickel aluminide (Ni₃Al or NiAl) formed byfirst electroplating nickel to the substrate layer 222 and then slurrycoating with aluminum and baking. Alternative coatings include at leastone of gold, platinum, iridium, nickel, and nickel-tungsten. Suchcoatings may be applied by electroplating, vapor deposition, or thermalspray.

Other coatings include oxides of yttrium, zirconium, hafnium, boron, andtheir combinations and may be formed by a thermal or a slurry coatingprocess. Yet other coatings may include combinations of the foregoingcoatings and processes.

One or more embodiments of the present invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, the relaxation resistant material layer may be located indiscrete locations along the length of the seal rather than continuouslyalong the length. Such refractory material may be localized to portionof the seal where the greatest flexing occurs. Accordingly, otherembodiments are within the scope of the following claims.

1. A process for manufacturing a seal for sealing between interior andexterior volumes when held under compression, comprising: cold formingan annular first seal layer; and applying a second layer to a firstsurface of the first layer via a process selected from the groupconsisting of: thermal spray of molten alloy droplets and powder;thermal spray of creep resistant alloys with ceramic particles; vapordeposition; slurry coating of ceramics and curing at elevatedtemperatures; electroforming of high temperature alloys; andcombinations thereof.
 2. The process of claim 1 wherein: the first layeris formed having a bellows-like section prior to the application of thesecond layer; and after the application of the second layer, there is nomachining step which removes a portion of the applied second layermaterial.
 3. The process of claim 2 wherein the step of cold formingcomprises one of: cutting an annulus from a tube and deforming theannulus to provide a radial section of enhanced compressibility; formingand welding a strip into an annulus and deforming the annulus to providea radial section of enhanced compressibility; and deforming a flat stripto provide a section of enhanced compressibility and further deformingand welding the strip to provide an annulus having a radial section ofenhanced compressibility.
 4. A process for manufacturing a seal having acentral longitudinal axis and forming a seal between interior andexterior volumes when held under compression between opposed first andsecond parallel faces of respective first and second flanges,comprising: cold forming an annular first seal layer from a refractorymaterial; and applying an oxidation resistant coating to the firstlayer.
 5. The process of claim 4 wherein the coating entirely covers thefirst seal layer.
 6. The process of claim 4 wherein the coatingcomprises at least one of molybdenum disilicide and nickel aluminide andis formed by a process including the acts of slurry coating of at leastone component of the coating and baking.
 7. The process of claim 4wherein the coating comprises at least a silicide is formed by a processincluding the acts of slurry coating of at least one component of thecoating and baking.
 8. The process of claim 4 wherein the coatingcomprises at least one of gold, platinum, and iridium is formed by aprocess including at least one of electroplating, vapor deposition orthermal spray.
 9. The process of claim 4 wherein the coating comprisesone or more oxides of yttrium, zirconium, hafnium, and boron.
 10. Aprocess for manufacturing an article, comprising: cold forming asubstrate from a first nickel- or cobalt-based superalloy; and applyinga coating of a γ′ hardened second nickel-based superalloy to thesubstrate.
 11. The process of claim 10 wherein the application is viathermal spray process and provides the coating having a thickness of atleast 10% of a thickness of the substrate.
 12. The process of claim 10wherein the article has a creep resistance at 982° C. greater than acold formed article of like dimensions consisting essentially of thefirst superalloy.
 13. The process of claim 10 wherein said substrate isformed from said first nickel-based superalloy.